Sections 2.1 - 2.4 Overview Wednesday, August 24, 2016 10:35 AM Chapter 2 : Atoms, Molecules, and Ions 2.1 | The Atomic Theory of Matter • Early greek philosophers like Democritus believed that the material world was made up of tine indivisible particles called "atomos" • Later Plato and Aristotle stated that these particles were not possible • John Dalton eventually formulated the notion off atoms that he used to measure amounts of atoms when they reacted with other substances ○ Dalton's Atomic Theory 1. Each element is composed of extremely small particles called atoms. 2. All atoms of a given element are identical, but the atoms of one element are different from the atoms of all other elements. 3. Atoms of one element cannot be changed into atoms of a different element by chemical reactions; atoms are neither created nordestroyed in chemical reactions. 4. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms. 2.2 | The Discoveryof Atomic Structure • The atoms is composed of subatomic particles : electrons, neutrons, and protons. ○ Cathode Rays and Electrons:  Electrical discharge through a glass tube, pumped empty air .  When a high voltage was applied to electrodes in tube, radiation was produced between electrodes.  This radiation is called cathode rays - where they originated at the negative electrode and traveled to the positive electrode